Novel endosomolytic peptides for enhancing gene delivery in nanoparticles

Endolysosomal trapping of therapeutics and endosomal escape strategies

Internalizing therapeutic molecules or genes into cells and safely delivering them to the target tissue where they can perform the intended tasks is one of the key characteristics of the smart gene/drug delivery vector. Despite much research in this field, endosomal escape continues to be a significant obstacle to the development of effective gene/drug delivery systems. In this review, we discuss in depth the several types of endocytic pathways involved in the endolysosomal trapping of therapeutic agents. In addition, we describe numerous mechanisms involved in nanoparticle endosomal escape. Furthermore, many other techniques are employed to increase endosomal escape to minimize entrapment of therapeutic compounds within endolysosomes, which have been reviewed at length in this study.

Melittin analog p5RHH enhances recombinant adeno-associated virus transduction efficiency

OBJECTIVE

Melittin and its derivative have been developed to support effective gene delivery systems. Their ability to facilitate endosomal release enhances the delivery of nanoparticle-based gene therapy. Nevertheless, its potential application in the context of viral vectors has not received much attention. Therefore, we would like to optimize the rAAV vector by Melittin analog to improve the transduction efficiency of rAAV in liver cancer cells and explore the mechanism of Melittin analog on rAAV.

METHODS

Various melittin-derived peptides were inserted into loop VIII of the capsid protein in recombinant adeno-associated virus vectors. These vectors carrying either gfp or fluc genes were subjected to quantitative polymerase chain reaction assays and transduction assays in human embryonic kidney 293 (HEK293T) cells to investigate the efficiency of vector production and gene delivery. In addition, the ability of a specific p5RHH-rAAV vector to deliver genes was examined through in vitro transduction of different cultured cells and in vivo tail vein administration to C57BL/6 mice. Finally, the intricate details of the vector-mediated transduction mechanisms were explored by using pharmacological inhibitors of every stage of the rAAV2 intracellular life cycle.

RESULTS

A total of 76 melittin-related peptides were identified from existing literature. Among them, CMA-3, p5RHH and aAR3 were found to significantly inhibit transduction of rAAV2 vector crude lysate. The p5RHH-rAAV2 vectors efficiently transduced not only rAAV-potent cell lines but also cell lines previously considered resistant to rAAV. Mechanistically, bafilomycin A1, a vacuolar endosome acidification inhibitor, completely inhibited the transgene expression mediated by the p5RHH-rAAV2 vectors. Most importantly, p5RHH-rAAV8 vectors also increased hepatic transduction in vivo in C57BL/6 mice.

CONCLUSION

The incorporation of melittin analogs into the rAAV capsids results in a significant improvement in rAAV-mediated transgene expression. While further modifications remain an area of interest, our studies have substantially broadened the pharmacological prospects of melittin in the context of viral vector-mediated gene delivery. Please cite this article as: Meng J, He Y, Yang H, Zhou L, Wang S, Feng X, Al-shargi OY, Yu X, Zhu L, Ling, C. Melittin analog p5RHH enhances recombinant adeno-associated virus transduction efficiency. J Integr Med. 2024; 22(1): 72-82.

Amino Acid-Coated Zeolitic Imidazolate Framework for Delivery of Genetic Material in Prostate Cancer Cell

Metal-organic frameworks (MOFs) are currently under progressive development as a tool for non-viral biomolecule delivery. Biomolecules such as proteins, lipids, carbohydrates, and nucleic acids can be encapsulated in MOFs for therapeutic purposes. The favorable physicochemical properties of MOFs make them an attractive choice for delivering a wide range of biomolecules including nucleic acids. Herein, a green fluorescence protein (GFP)-expressing plasmid DNA (pDNA) is used as a representative of a biomolecule to encapsulate within a Zn-based metal-organic framework (MOF) called a zeolitic imidazolate framework (ZIF). The synthesized biocomposites are coated with positively charged amino acids (AA) to understand the effect of surface functionalization on the delivery of pDNA to prostate cancer (PC-3) cells. FTIR and zeta potential confirm the successful preparation of positively charged amino acid-functionalized derivatives of pDNA@ZIF (i.e., pDNA@ZIF_AA). Moreover, XRD and SEM data show that the functionalized derivates retain the pristine crystallinity and morphology of pDNA@ZIF. The coated biocomposites provide enhanced uptake of genetic material by PC-3 human prostate cancer cells. The AA-modulated fine-tuning of the surface charge of biocomposites results in better interaction with the cell membrane and enhances cellular uptake. These results suggest that pDNA@ZIF_AA can be a promising alternative tool for non-viral gene delivery.

Endosomal escape for cell-targeted proteins. Going out after going in

Protein-based nanocarriers are versatile and biocompatible drug delivery systems. They are of particular interest in nanomedicine as they can recruit multiple functions in a single modular polypeptide. Many cell-targeting peptides or protein domains can promote cell uptake when included in these nanoparticles through receptor-mediated endocytosis. In that way, targeting drugs to specific cell receptors allows a selective intracellular delivery process, avoiding potential side effects of the payload. However, once internalized, the endo-lysosomal route taken by the engulfed material usually results in full degradation, preventing their adequate subcellular localization, bioavailability and subsequent therapeutic effect. Thus, entrapment into endo-lysosomes is a main bottleneck in the efficacy of protein-drug nanomedicines. Promoting endosomal escape and preventing lysosomal degradation would make this therapeutic approach clinically plausible. In this review, we discuss the mechanisms intended to evade lysosomal degradation of proteins, with the most relevant examples and associated strategies, and the methods available to measure that effect. In addition, based on the increasing catalogue of peptide domains tailored to face this challenge as components of protein nanocarriers, we emphasize how their particular mechanisms of action can potentially alter the functionality of accompanying protein materials, especially in terms of targeting and specificity in the delivery process.

Melittin-Based Nano-Delivery Systems for Cancer Therapy

Melittin (MEL) is a 26-amino acid polypeptide with a variety of pharmacological and toxicological effects, which include strong surface activity on cell lipid membranes, hemolytic activity, and potential anti-tumor properties. However, the clinical application of melittin is restricted due to its severe hemolytic activity. Different nanocarrier systems have been developed to achieve stable loading, side effects shielding, and tumor-targeted delivery, such as liposomes, cationic polymers, lipodisks, etc. In addition, MEL can be modified on nano drugs as a non-selective cytolytic peptide to enhance cellular uptake and endosomal/lysosomal escape. In this review, we discuss recent advances in MEL’s nano-delivery systems and MEL-modified nano drug carriers for cancer therapy.

Antimicrobial peptide-based materials: opportunities and challenges

The multifunctional properties of antimicrobial peptides (AMPs) make them attractive candidates for the treatment of various diseases. AMPs are considered alternatives to antibiotics due to the rising number of multidrug-resistant...

Enhanced gene expression by a novel designed leucine zipper endosomolytic peptide

An endosomal trap is a major barrier in gene therapy. We have designed an endosomolytic peptide based on the leucine zipper sequence and characterized it both structurally and functionally. The results illustrated that leucine zipper endosomolytic peptide (LZEP) exhibited appreciable hemolysis of human red blood cells (hRBCs) at pH 5.0, but negligible hemolysis at pH 7.4. Calcein release experiment indicated that only at pH 5.0 but not at pH 7.4, LZEP was able to permeabilize hRBCs. LZEP revealed significant self-assembly as well as peptide induced α-helical structure at pH 5.0. Unlike at pH 5.0, LZEP failed to self-assemble and showed a random coil structure at pH 7.4. Transfection data depicted that lipoplexes modified with LZEP resulted in significantly higher gene expression as compared to lipoplexes without LZEP. Interestingly, the transfection efficacy of LZEP modified lipid nanoparticles reached the levels of Lipofectamine 2000 (LF 2000), without any cellular toxicity as observed by MTT assay. The results suggest a novel approach for designing endosomolytic peptides by employing the leucine zipper sequence and simultaneously the designed peptides could be utilized for enhancing gene delivery into mammalian cells.

Rational Modulation of pH-Triggered Macromolecular Poration by Peptide Acylation and Dimerization

The synthetically evolved pH-dependent delivery (pHD) peptides are a unique family that bind to membranes, fold into α-helices, and form macromolecule-sized pores at low concentration at pH < 6. These peptides have potential applications in drug delivery and tumor targeting. Here, we show how pHD peptide activity can be modulated without changing the amino acid sequence. We increased the hydrophobicity of a representative peptide, pHD108 (GIGEVLHELAEGLPELQEWIHAAQQLGC-amide), by coupling hydrophobic acyl groups of 6-16 carbons and by forming dimers. Unlike the parent peptide, almost all variants showed activity at pH 7. This was due to strong partitioning into phosphatidylcholine vesicle bilayers and induced helix formation. The dimer maintained some pH sensitivity while being the most active peptide studied in this work, with macromolecular poration occurring at 1:2000 peptide:lipid at pH 5. These results confirm that membrane binding, rather than pH, is the determining factor in activity, while also showing that acylation and dimerization are viable methods to modulate pHD108 activity. We propose a possible toroidal pore architecture with peptides in a parallel or mixed parallel/antiparallel orientation without strong electrostatic interactions between peptides in the pore as evidenced by a lack of dependence of activity on either pH or salt concentration.

Tailoring Iron Oxide Nanoparticles for Efficient Cellular Internalization and Endosomal Escape

Iron oxide nanoparticles (IONs) have been widely explored for biomedical applications due to their high biocompatibility, surface-coating versatility, and superparamagnetic properties. Upon exposure to an external magnetic field, IONs can be precisely directed to a region of interest and serve as exceptional delivery vehicles and cellular markers. However, the design of nanocarriers that achieve an efficient endocytic uptake, escape lysosomal degradation, and perform precise intracellular functions is still a challenge for their application in translational medicine. This review highlights several aspects that mediate the activation of the endosomal pathways, as well as the different properties that govern endosomal escape and nuclear transfection of magnetic IONs. In particular, we review a variety of ION surface modification alternatives that have emerged for facilitating their endocytic uptake and their timely escape from endosomes, with special emphasis on how these can be manipulated for the rational design of cell-penetrating vehicles. Moreover, additional modifications for enhancing nuclear transfection are also included in the design of therapeutic vehicles that must overcome this barrier. Understanding these mechanisms opens new perspectives in the strategic development of vehicles for cell tracking, cell imaging and the targeted intracellular delivery of drugs and gene therapy sequences and vectors.

Antimicrobial peptide AR-23 derivatives with high endosomal disrupting ability enhance poly(l-lysine)-mediated gene transfer

Background

pH‐sensitive peptides are a relatively new strategy for conquering the poor endosomal release of cationic polymer‐mediated transfection. Modification of antimicrobial peptides by exchanging positively‐charged residues with negatively‐charged glutamic acid residues (Glu) greatly improves its lytic activity at the endosomal pH, which could improve cationic polymer‐mediated transfection.

Methods

In the present study, we investigated the effect of the number of Glu substituted for positively‐charged residues on the endosomal escape activity of AR‐23 and the ability of mutated AR‐23 with respect to enhancing cationic polymer‐mediated transfection. Three analogs were synthesized by replacing the positively‐charged residues in the AR‐23 sequence with Glu one‐by‐one.

Results

The pH‐sensitive lysis ability of the peptides, the effect of peptides on the physicochemical characteristics, the intracellular trafficking, the transfection efficiency and the cytotoxicity of the polyplexes were determined. Increased lytic activity of peptides was observed with the increased number of Glu replacement in the AR‐23 sequence at acidic pH. The number of Glu substituted for positively‐charged residues of AR‐23 dramatically affects its lysis ability at neutral pH. Triple‐Glu substitution in the AR‐23 sequence greatly improved poly(l‐lysine)‐mediated gene transfection efficiency at the same time as maintaining low cytotoxicity.

Conclusions

The results indicate that replacement of positively‐charged residues with sufficient Glu residues may be considered as a method for designing pH‐sensitive peptides, which could be applied as potential enhancers for improving cationic polymer‐mediated transfection.

Ligand targeting and peptide functionalized polymers as non-viral carriers for gene therapy

Ligand targeting and peptide functionalized polymers serve as gene carriers for efficient gene delivery.

Optimization of peptide-plasmid DNA vectors formulation for gene delivery in cancer therapy exploring design of experiments

The field of gene therapy still attracts great interest due to its potential therapeutic effect towards the most deadly diseases, such as cancer. For cancer gene therapy to be feasible and viable in a clinical setting, the design and development of a suitable gene delivery system is imperative. Peptide based vectors, in particular, reveal to be promising for therapeutic gene release. Following this, two different peptides, RALA and WRAP5, have been investigated mainly regarding their ability to form complexes with a p53 encoding plasmid (pDNA) with suitable properties for gene delivery. To address this issue, and after an initial screening study focused on the dependence of pDNA complexation capacity with the nitrogen to phosphate groups (N/P) ratio, a design of experiments (DoE) tool has been employed. For each peptide/pDNA system, parameters such as, the buffer pH and the N/P ratio were considered the DoE inputs and the vector size, zeta potential and pDNA complexation capacity (CC) were monitored as DoE outputs. The main goal was to find the optimal experimental conditions to minimize particle sizes, as well as, to maximize the positive surface charges of the formulated nanosystems and maximize the pDNA CC. Through the DoE method applied, the optimal RALA/pDNA and WRAP5/pDNA formulations were revealed and show interesting features related to peptide structure and pDNA complexation ability. This work illustrates the great utility of experimental design tools in optimizing the formulation of peptide/pDNA vectors in a minimum number of experiments providing relevant knowledge for the development of more suitable and efficient gene delivery systems. The new insights achieved on these carriers clearly instigate deeper research on gene therapy.

Novel Peptide Conjugates of Modified Oligonucleotides for Inhibition of Bacterial RNase P

Novel alternatives to traditional antibiotics are now of great demand for the successful treatment of microbial infections. Here, we present the engineering and properties of new oligonucleotide inhibitors of RNase P, an essential bacterial enzyme. The series of 2’-O-methyl RNA (2’-OMe-RNA) and phosphoryl guanidine oligonucleotides were targeted to the substrate-binding region of M1 RNA subunit of the RNase P. Uniformly modified 2’-OMe RNA and selectively modified phosphoryl guanidine oligonucleotides possessed good stability in biological media and effectively inhibited RNase P. Their conjugates with transporting peptides were shown to penetrate bacterial cells (Escherichia coli and Acinetobacter baumannii) and inhibit bacterial growth.

Anti-Tumor Effects of Melittin and Its Potential Applications in Clinic

Melittin, a major component of bee venom, is a water-soluble toxic peptide of which a various biological effects have been identified to be useful in anti-tumor therapy. In addition, Melittin also has anti-parasitic, anti-bacterial, anti-viral, and anti-inflammatory activities. Therefore, it is a very attractive therapeutic candidate for human diseases. However, melittin induces extensive hemolysis, a severe side effect that dampens its future development and clinical application. Thus, studies of melittin derivatives and new drug delivery systems have been conducted to explore approaches for optimizing the efficacy of this compound, while reducing its toxicity. A number of reviews have focused on each side, respectively. In this review, we summarize the research progress on the anti-tumor effects of melittin and its derivatives, and discuss its future potential clinical applications.

Cationic block amphiphiles show anti-mitochondrial activity in multi-drug resistant breast cancer cells

Currently, there are limited treatment options for multi-drug resistant breast cancer. Lipid-modified cationic peptides have the potential to reach the mitochondria, which are attractive targets for the treatment of multi-drug resistant (MDR) breast cancer; yet, little is known about their mitochondrial targeting and anti-cancer activity. Interestingly, lipid-modified cationic peptides, typically used as gene transfection agents, exhibit similar structural features to mitochondrial targeted peptides. Using octahistidine-octaarginine (H₈R₈) as a model cationic peptide for cell penetration and endosomal escape, we explored the anti-cancer potential of lipid-modified cationic peptides as a function of amphiphilicity, biodegradability and lipid structure. We found that cationic peptides modified with a lipid that is at least 12 carbons in length exhibit potent anti-cancer activity in the low micromolar range in both EMT6/P and EMT6/AR-1 breast cancer cells. Comparing degradable and non-degradable linkers, as well as L- and D-amino acid sequences, we found that the anti-cancer activity is mostly independent of the biodegradation of the lipid-modified cationic peptides. Two candidates, stearyl-H₈R₈ (Str-H₈R₈) and vitamin E succinate-H₈R₈ (VES-H₈R₈) were cytotoxic to cancer cells by mitochondria depolarization. We observed increased reactive oxygen species (ROS) production, reduced cell bioenergetics and drug efflux, triggering apoptosis and G1 cell cycle arrest. Compared to Str-H₈R₈, VES-H₈R₈ showed enhanced cancer cell selectivity and drug efflux inhibition, thereby serving as a potential novel therapeutic agent. This study deepens our understanding of lipid-modified cationic peptides and uncovers their potential in multi-drug resistant breast cancer.

Antibody Delivery for Intracellular Targets: Emergent Therapeutic Potential

Proteins have sparked fast growing interest as biological therapeutic agents for several diseases. Antibodies, in particular, carry an enormous potential as drugs owing to their remarkable target specificity and low immunogenicity. Although the market has numerous antibodies directed toward extracellular targets, their use in targeting therapeutically important intracellular targets is limited by their inability to cross cellular membrane. Realizing the potential for antibody therapy in disease treatment, progress has been made in the development of methods to deliver antibodies intracellularly. In this review, we address various platforms for delivery of antibodies and their merits and drawbacks.

Current Challenges in Delivery and Cytosolic Translocation of Therapeutic RNAs

RNA interference (RNAi) is a fundamental cellular process for the posttranscriptional regulation of gene expression. RNAi can exogenously be modulated by small RNA oligonucleotides, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), or by antisense oligonucleotides. These small oligonucleotides provided the scientific community with powerful and versatile tools to turn off the expression of genes of interest, and hold out the promise of new therapeutic solutions against a wide range of gene-associated pathologies. However, unmodified nucleic acids are highly instable in biological systems, and their weak interaction with plasma proteins confers an unfavorable pharmacokinetics. In this review, we first provide an overview of the most efficient chemical strategies that, over the past 30 years, have been used to significantly improve the therapeutic potential of oligonucleotides. Oligonucleotides targeting and delivery technologies are then presented, including covalent conjugates between oligonucleotides and targeting ligand, and noncovalent association with lipid or polymer nanoparticles. Finally, we specifically focus on the endosomal escape step, which represents a major stumbling block for the effective use of oligonucleotides as therapeutic agents. The need for approaches to quantitatively measure endosomal escape and cytosolic arrival of biomolecules is discussed in the context of the development of efficient oligonucleotide targeting and delivery vectors.

Molecular determinants for cyclo-oligosaccharide-based nanoparticle-mediated effective siRNA transfection

AIM

To study the structural requirements that a cyclooligosaccharide-based nanoparticle must fulfill to be an efficient siRNA transfection vector.

MATERIALS & METHODS

siRNA protection from degradation by RNAses, transfection efficiency and the thermodynamic parameters of the nanoparticle/siRNA interactions were studied on pairs of amphiphilic molecules using biochemical techniques and molecular dynamics.

RESULTS

The lower the siRNA solvent accessible surface area in the presence of the nanoparticle, higher the protection from RNAse-mediated degradation in the corresponding nanocomplex; a moderate nanoparticle/siRNA binding energy value further facilitates reversible complexation and binding to the target cellular mRNA.

CONCLUSION

The use, in advance, of these parameters will provide a useful indication of the potential of a molecular nanoparticle as siRNA transfecting vector.

Effect of Linker Length on Cell Capture by Poly(ethylene glycol)-Immobilized Antimicrobial Peptides

Development of antimicrobial peptide (AMP)-functionalized materials has renewed interest in using poly(ethylene glycol) (PEG)-mediated linking to minimize unwanted interactions while engendering the peptides with sufficient flexibility and freedom of movement to interact with the targeted cell types. While PEG-based linkers have been used in many AMP-based materials, the role of the tether length has been minimally explored. Here, we assess the impact of varying the length of PEG-based linkers on the binding of bacterial cells by surface-immobilized AMPs. While higher surface densities of immobilized AMPs were observed using shorter PEG linkers, the increased density was insufficient to fully account for the increased binding activity of peptides. Furthermore, effects were specific to both the peptide and cell type tested. These results suggest that simple alterations in linking strategies-such as changing tether length-may result in large differences in the surface properties of the immobilized AMPs that are not easily predictable.

Human Antimicrobial Peptides in Bodily Fluids: Current Knowledge and Therapeutic Perspectives in the Postantibiotic Era

Antimicrobial peptides (AMPs) are an integral part of the innate immune defense mechanism of many organisms. Due to the alarming increase of resistance to antimicrobial therapeutics, a growing interest in alternative antimicrobial agents has led to the exploitation of AMPs, both synthetic and isolated from natural sources. Thus, many peptide-based drugs have been the focus of increasing attention by many researchers not only in identifying novel AMPs, but in defining mechanisms of antimicrobial peptide activity as well. Herein, we review the available strategies for the identification of AMPs in human body fluids and their mechanism(s) of action. In addition, an overview of the distribution of AMPs across different human body fluids is provided, as well as its relation with microorganisms and infectious conditions.

Inner ear barriers to nanomedicine-augmented drug delivery and imaging

There are several challenges to inner ear drug delivery and imaging due to the existence of tight biological barriers to the target structure and the dense bone surrounding it. Advances in imaging and nanomedicine may provide knowledge for overcoming the existing limitations to both the diagnosis and treatment of inner ear diseases. Novel techniques have improved the efficacy of drug delivery and targeting to the inner ear, as well as the quality and accuracy of imaging this structure. In this review, we will describe the pathways and biological barriers of the inner ear regarding drug delivery, the beneficial applications and limitations of the imaging techniques available for inner ear research, the behavior of engineered nanomaterials in inner ear applications, and future perspectives for nanomedicine-based inner ear imaging.

In vitro and in vivo assessment of chitosan modified urocanic acid as gene carrier

Chitosan nanoparticles modified with 10 and 30% urocanic acid (CUA) via carbodiimide crosslinking were examined for an efficient gene delivery carrier. The CUA gene carrier was characterized by FTIR, TEM, SEM and the in vitro transfection efficiency CUA polyplex was tested with HeLa and 3T3 cells. The loading efficiency of CUA complexes with DNA was assessed at different N/P ratio of 1, 2, 4, 6, 8, and 10. The DNA loading efficiency was found be to >85% for chitosan, CUA10 and CUA30% and the DNA protection ability of CUA10 and CUA30 nanoparticle complexes was confirmed upon incubation with NheI and HindIII. The cell toxicity and cell viability results have supported the non-toxic nature of CUA10 and CUA30 nanoparticles. In vitro transfection efficiency of CUA10 and CUA30 polyplex was tested for EGFP expression in 3T3 and HeLa cells and a relative maximum % transfection of about 10% was confirmed by CUA10 and CUA30 after 96h transfection. The feasibility and biocompatibility of CUA gene carrier in transgenic chickens was also demonstrated. The in vitro transfection and in vivo embryonic viability studies further confirmed the CUA as promising gene carrier because of the improved biocompatibility and DNA protection ability.

An Overview of Nanoparticle Based Delivery for Treatment of Inner Ear Disorders

Nanoparticles offer new possibilities for inner ear treatment as they can carry a variety of drugs, protein, and nucleic acids to inner ear. Nanoparticles are equipped with several functions such as targetability, immuno-transparency, biochemical stability, and ability to be visualized in vivo and in vitro. A group of novel peptides can be attached to the surface of nanoparticles that will enhance the cell entry, endosomal escape, and nuclear targeting. Eight different types of nanoparticles with different payload carrying strategies are available now. The transtympanic delivery of nanoparticles indicates that, depending on the type of nanoparticle, different migration pathways into the inner ear can be employed, and that optimal carriers can be designed according to the intended cargo. The use of nanoparticles as drug/gene carriers is especially attractive in conjunction with cochlear implantation or even as an inclusion in the implant as a drug/gene reservoir.

Contact-facilitated drug delivery with Sn2 lipase labile prodrugs optimize targeted lipid nanoparticle drug delivery

Sn2 lipase labile phospholipid prodrugs in conjunction with contact-facilitated drug delivery offer an important advancement in Nanomedicine. Many drugs incorporated into nanosystems, targeted or not, are substantially lost during circulation to the target. However, favorably altering the pharmacokinetics and volume of distribution of systemic drug delivery can offer greater efficacy with lower toxicity, leading to new prolonged-release nanoexcipients. However, the concept of achieving Paul Erhlich's inspired vision of a 'magic bullet' to treat disease has been largely unrealized due to unstable nanomedicines, nanosystems achieving low drug delivery to target cells, poor intracellular bioavailability of endocytosed nanoparticle payloads, and the substantial biological barriers of extravascular particle penetration into pathological sites. As shown here, Sn2 phospholipid prodrugs in conjunction with contact-facilitated drug delivery prevent premature drug diffusional loss during circulation and increase target cell bioavailability. The Sn2 phospholipid prodrug approach applies equally well for vascular constrained lipid-encapsulated particles and micelles the size of proteins that penetrate through naturally fenestrated endothelium in the bone marrow or thin-walled venules of an inflamed microcirculation. At one time Nanomedicine was considered a 'Grail Quest' by its loyal opposition and even many in the field adsorbing the pains of a long-learning curve about human biology and particles. However, Nanomedicine with innovations like Sn2 phospholipid prodrugs has finally made 'made the turn' toward meaningful translational success.

Nanoparticles incorporating pH-responsive surfactants as a viable approach to improve the intracellular drug delivery

The pH-responsive delivery systems have brought new advances in the field of functional nanodevices and might allow more accurate and controllable delivery of specific cargoes, which is expected to result in promising applications in different clinical therapies. Here we describe a family of chitosan-TPP (tripolyphosphate) nanoparticles (NPs) for intracellular drug delivery, which were designed using two pH-sensitive amino acid-based surfactants from the family N(α),N(ε)-dioctanoyl lysine as bioactive compounds. Low and medium molecular weight chitosan (LMW-CS and MMW-CS, respectively) were used for NP preparation, and it was observed that the size distribution for NPs with LMW-CS were smaller (~168 nm) than that for NPs prepared with MMW-CS (~310 nm). Hemolysis assay demonstrated the pH-dependent biomembrane disruptional capability of the constructed NPs. The nanostructures incorporating the surfactants cause negligible membrane permeabilization at pH7.4. However, at acidic pH, prevailing in endosomes, membrane-destabilizing activity in an erythrocyte lysis assay became evident. When pH decreased to 6.6 and 5.4, hemolytic capability of chitosan NPs increased along with the raise of concentration. Furthermore, studies with cell culture showed that these pH-responsive NPs displayed low cytotoxic effects against 3T3 fibroblasts. The influence of chitosan molecular weight, chitosan to TPP weight ratio, nanoparticle size and nature of the surfactant counterion on the membrane-disruptive properties of nanoparticles was discussed in detail. Altogether, the results achieved here showed that by inserting the lysine-based amphiphiles into chitosan NPs, pH-sensitive membranolytic and potentially endosomolytic nanocarriers were developed, which, therefore, demonstrated ideal feasibility for intracellular drug delivery.

Antimicrobial peptides in 2014

This article highlights new members, novel mechanisms of action, new functions, and interesting applications of antimicrobial peptides reported in 2014. As of December 2014, over 100 new peptides were registered into the Antimicrobial Peptide Database, increasing the total number of entries to 2493. Unique antimicrobial peptides have been identified from marine bacteria, fungi, and plants. Environmental conditions clearly influence peptide activity or function. Human α-defensin HD-6 is only antimicrobial under reduced conditions. The pH-dependent oligomerization of human cathelicidin LL-37 is linked to double-stranded RNA delivery to endosomes, where the acidic pH triggers the dissociation of the peptide aggregate to release its cargo. Proline-rich peptides, previously known to bind to heat shock proteins, are shown to inhibit protein synthesis. A model antimicrobial peptide is demonstrated to have multiple hits on bacteria, including surface protein delocalization. While cell surface modification to decrease cationic peptide binding is a recognized resistance mechanism for pathogenic bacteria, it is also used as a survival strategy for commensal bacteria. The year 2014 also witnessed continued efforts in exploiting potential applications of antimicrobial peptides. We highlight 3D structure-based design of peptide antimicrobials and vaccines, surface coating, delivery systems, and microbial detection devices involving antimicrobial peptides. The 2014 results also support that combination therapy is preferred over monotherapy in treating biofilms.